I always try for a negative split (slower first half than second half). It's always better to have that extra energy to burn - which feels better: passing 50 people during your last five miles of the half marathon or getting passed by 50 people? Most people start out too fast - just let them pass you and smile as they do. Deep down you'll know that you will pass them in mile 10.

Have you tried running with a club?

There's usually someone there who takes it upon themselves to rein in the speed on longer runs.

Everyone can run much longer on a treadmill though. That's not unique to you. I always wondered just how much of a marketing ploy that was - "I love my Acme Fitrun machine - I can do 12 miles in just under 1:30!" Meanwhile that person finishes a half marathon in 3:14.

Think about the physics of running on a treadmill. The only part of your body constantly accelerating are your legs - your upper body hardly moves. When running outside, you have air resistance, speeding up / slowing down to avoid obstacles, slight side-movements .... Your body simply is working harder.